I would agree with your research, I am certain that it is Fomes fomentarius - Hoof Fungus. Common in Scotland, and northern England, becoming progressively rarer as you travel south.
Here are some that I photographed in the Great Glen, Scotland, when kayaking.
and a fresh one...
Apparently it can be used by trout fishermen to dry their ...
Also known as Bolbitius vitellinus, that there looks to be a young Yellow Field Cap. They're quite small when they're yellow, but they quickly mature into taller, flatter, brownish mushroom.
Those look like oyster mushrooms. They are the right size and color and have the right type of gills.
Pleurotus ostreatus, is a common edible known for its oyster-shaped cap. One of the first things you should look for when trying to identify this mushroom is the presence of decurrent gills.
Decurrent means that the gills are attached to and run ...
Chaga is parasitic and grows exclusively on living trees.
The tree you have pictured appears to be rotting. Additionally, the mushrooms on that tree have a clear top and bottom. Although the coloration is similar, the picture above does not appear to be Chaga.
I will, however, do some research to see if I can find what fungus in fact is growing.
To be honest, I'm not sure we have enough information here to help you in this case. There are many different kinds of puffballs, some are edible, some are not. Depending on the age they will also vary wildly in their look and consistency, so this makes it even harder.
I can really only recommend two ways to identify mushroom:
Get a decent book
Buy a ...
Hard to tell from photo, but: "gills" look yellow which is wrong for a button /agaricus compestri . Do they have gills ? If they have a spongy matter and not gills they are likely some boletin . Usually found under conifers. If so, likely edible but not much flavor.